OK, first off the typical apologies. I play on suicidal. I play on maps with all abundant settings. I play with very fast research (and turn tech victories off). This does mean that I get into wars with everyone maxed in the tech tree with some regularity. I am used to wars at this level, and it makes up about half of my combat experience in DA.
I (finally) got around to running a game where I was in some real wars, and had to work to stay alive. My main enemy was the drengin (+55% weapons, +35% def, +81% hp) - and I had taken all combat stats with my starting points (+20wep/+30def/+30hp) and had one fully upgraded military starbase (+55% weapons, +160% def, +80% hp). I also had 3 Hyperion Shrinkers. Combat came down to fleets of five on five of the following two vessels:

Now, in a one on one, I won this battle while taking very little damage. This meant that all drengin worlds without an Oribital Fleet Manager were mine, I could endlessly pick off the defenders.
But fleet on fleet it was another matter. I had fleet attack values of 1155, they had fleet attack values of 4275. When our sides met... the typical outcome was:
Round 1: I destroy 2 ships, they destroy 2 ships
Round 2: I destroy 2 ships, they destroy 1 ship
Round 3: I destroy 1 ship, they destroy 0 ships
So I was trading 3 defensive ships for 5 attack ships. My best pure attack ship was a 560 attack (I still don't get how they managed over 800 attack per ship, what must that miniturization bonus have been... and I had 3 shrinkers!), so I couldn't trade attack ships with them because I lost all battles based on the tie rule. I would always lose 5 to their 4, or I would just straight up lose in a one on one.
Trying to increase my damage by adding attack ships to my fleet only increased my losses. Pure attack ships were targeted first, and only had 150 some hps to defend themselves. If I switched out 1 def for 1 attack ship, my attack would rise to 1500 - but combat proceeded:
Round 1: I destroy 3 ships, they destroy 3 ships
Round 2: I destroy 1 ship, they destroy 1 ship
Round 3: I destroy 1 ship, they destroy 0 ships
So I would then only be surviving with 1 ship per engagement.
These losses were higher than I would like, but I just couldn't get down to losing only 2 ships to their five. If I sent in 3 pure attack ships I could do enough damage to knock out all five in one round, but my 3 attack ships would all die and they would survive with one: a 3 to 4 ratio (worse). If I sent in one kamikaze attack ship I could usually knock out two enemy ships, and then if I followed up with a full defensive fleet I would sometimes lose only one ship in the second battle, but more often I would lose 2 ships - and then I was back to my three losses.
The real problem was taking out Orbital Fleet Manager worlds. On these, the Drengin attack would go up to a 1037 per ship, so then I was facing 5100 attack. Trying to take those worlds combat would go:
Round 1: I destroy 2 ships, they destroy 3 ships
Round 2: I destroy 1 ship, they destroy 2 ships
And I was losing production points. Here, it was better to send in fleets of 3 suicide all attack ships and then follow up with my full defensive fleet, but again I'm trading 3 ships for 5.
Ultimately, I didn't like the losses I was forced to suffer facing those fleets, so I just took every Drengin world without an OFM, and built them full of fertility clinics and cultural centers. If the Drengin retook them, they were worthless hunks with little research or industry, but if they didn't retake them I could culture flip the worlds with OFMs so that I didn't have to try and blast through those 5k attack super defense fleets.
I prefer setups where I take no losses (earlier I had faced Iconians with ships similar to mine - we couldn't hurt each other but I had slightly higher attack values and so due to the tie rule I would always wipe them out. When you destroy 5 huge hulls per move and take no losses, you know you are doing something right). Still, my fleets were performing 66% better than the Drengin when I was using matching defense oriented ships. Not unkillable, but acceptable losses.
Interestingly, the very first war in the whole game was between the Korx and the Thalans. The Korx had a one level logistics advantage, the Thalans had a hull size advantage. The Thalans had huge hulls with 50 attack/50 defense in fleets of 3 (24 logistics) - the Korx had medium hulls with 30 attack/30 defense in fleets of 9 (37 logistics). The Korx handily beat the Thalans, only losing one or two medium fighters per engagement. It is not often I get to watch smaller hulls beat up on larger hulls, so it was fun to watch.
Overall:
Several things - the tie rule still dictates the outcome of about half of the fights, and the game is much harder when the AI can build ships you can't match. It seems no matter what I do my ships are underpowered vs what the AI is building at Suicidal - Early on I don't have a tech advantage, later on their natural bonuses take their ship building beyond what is even possible for me.
Offensive fleets can still dominate any opponent, but you will pay a price (in industrial units) for using that strategy.
Huge hulls dominate the galaxy. The other sizes can't compete (maybe they shouldn't be able to, I like capital ships being a "big deal"). If the AI would fleet its huge hulls with anything but a top of the line large, the whole fleet became a sitting duck to a full fleet of five huges. Drengin super dominator corvettes would really hurt it, because it insisted on fleeting them with its dreadnaughts, sometimes taking its fleet attack value all the way down to around 2000 from over 4200. That makes a big difference when you are fighting defense oriented fleets. Fleets with such a low attack value are ripe for the picking.
I wish spies could take out OFM, but overall they are probably better used attacking farms because...
The AI is still reasonably poor at building transports and taking worlds. Personally, I make ship transport building worlds that just crank out transports and launch them all game. My typical setup on a PQ10 world would be: 2 farms, 3 fertility acceleration, 1 starport, 2 industrial centers, 1 VR center. With two of these in an empire it is not hard to get upwards of 100billion soldiers sitting in transports waiting for enemy defenses to fall.
Also, the AI seems to not try and rebuild over tiles. First - once the tech tree is finished (with tech victory off) - they have no need for all of those discovery spheres they have sitting around. Second, when the AI would retake a world filled with my cultural centers, they wouldn't start building over what I had done. 10 turns later I could retake the world and there wasn't even a building queued up. That worked great for me... but was poor for them.
Compared to what I was experiencing when DA was first released, I am much happier with this game balance. I understand that before the tech tree is maxed players can use tech advantages from just about anywhere in the combat tree to their advantage. But in the end, it all evens out.